1. Field of the Invention
The present invention relates to a device of and a method for detecting three-phase alternating currents of two different frequencies, and more particularly, to a current detecting device and a current detecting method that permit a reduction in the number of current detecting sensors.
2. Description of the Related Art
Generally, in detection of a three-phase alternating current, once U- and V-phase currents are detected, a W-phase can be computed by xe2x80x94(U-phase+V-phase). Hence, a three-phase alternating current can be detected by using two current detecting sensors. Detecting three-phase alternating currents of two different frequencies has been requiring a total of four current detecting sensors to detect the U- and V-phase currents of each three-phase alternating current.
A current detecting device having a configuration mentioned above requires four expensive current detecting sensors, leading to increased cost.
The present invention has been made to solve the above problem, and it is an object of the present invention to provide a current detecting device and a current detecting method that allow three-phase alternating currents of two different frequencies to be detected only by two current detecting sensors, thereby achieving reduced cost.
To this end, according to one aspect of the present invention, there is provided a current detecting device, including:
current detecting means for simultaneously detecting a plurality of three-phase alternating currents of different frequencies that are respectively output from two windings of a dynamo-electric machine having two windings wrapped around the same stator core;
estimating means for obtaining estimated values of the respective currents; and
separation computing means for separating, by each frequency, currents detected by the current detecting means based on outputs of the estimating means.
In a preferred form, the separation computing means includes:
two-phase alternating current converting means for converting a current detected by the current detecting means into a two-phase alternating current;
reverse rotation vector multiplying means for multiplying a value obtained by the two-phase alternating current converting means by a vector that rotates in a reverse direction at each frequency; and
multiplied frequency difference vector subtracting means for subtracting an estimated value multiplied by a vector that rotates at a difference between frequencies from an output of the reverse rotation vector multiplying means.
In another preferred form, the current detecting means includes:
first current detecting means for simultaneously detecting a first phase current of a first alternating current and a first phase current of a second alternating current;
second current detecting means for simultaneously detecting a second phase current of the first alternating current and a second phase current of the second alternating current; and
the separation computing means includes:
two-phase alternating current converting means for converting an output of the first current detecting means and an output of the second current detecting means into two-phase alternating currents;
first reverse rotation vector multiplying means for multiplying an output of the two-phase alternating current converting means by a unit vector rotating in a reverse direction at a frequency of the first alternating current;
second reverse rotation vector multiplying means for multiplying an output of the two-phase alternating current converting means by a unit vector rotating in a reverse direction at a frequency of the second alternating current;
first frequency difference vector multiplying means for multiplying an estimated value of the first alternating current by a unit vector rotating at (a frequency of the first alternating current minus a frequency of the second alternating current);
first vector subtracting means for subtracting an output of the first frequency difference vector multiplying means from an output of the second reverse rotation vector multiplying means;
second frequency difference vector multiplying means for multiplying an estimated value of the second alternating current by a unit vector rotating at (a frequency of the second alternating current minus a frequency of the first alternating current); and
second vector subtracting means for subtracting an output of the second frequency difference vector multiplying means from an output of the first reverse rotation vector multiplying means.
In yet another preferred form, the current detecting means includes:
first current detecting means for simultaneously detecting a first phase current of a first alternating current and a first phase current of a second alternating current;
second current detecting means for simultaneously detecting a second phase current of the first alternating current and a second phase current of the second alternating current; and
the separation computing means includes:
two-phase alternating current converting means for converting an output of the first current detecting means and an output of the second current detecting means into two-phase alternating currents;
first reverse rotation vector multiplying means for multiplying an output of the two-phase alternating current converting means by a unit vector rotating in a reverse direction at a frequency of the first alternating current;
second reverse rotation vector multiplying means for multiplying an output of the two-phase alternating current converting means by a unit vector rotating in a reverse direction at a frequency of the second alternating current;
first estimated value subtracting means for subtracting an estimated value of the first alternating current from an output of the first reverse rotation vector multiplying means;
first frequency difference vector multiplying means for multiplying an output of the first estimated value subtracting means by a unit vector rotating at (a frequency of the first alternating current minus a frequency of the second alternating current);
second estimated value subtracting means for subtracting an estimated value of the second alternating current from an output of the second reverse rotation vector multiplying means; and
second frequency difference vector multiplying means for multiplying an output of the second estimated value subtracting means by a unit vector rotating at (a frequency of the second alternating current minus a frequency of the first alternating current).
The estimated value of the first alternating current and the estimated value of the second alternating current are current command values.
The estimated value of the first alternating current and the estimated value of the second alternating current are first-order lags of the outputs of the first vector subtracting means and the second vector subtracting means.
The estimated value of the first alternating current and the estimated value of the second alternating current are first-order lags of the outputs of the first frequency difference vector multiplying means and the second frequency difference vector multiplying means.
According to another aspect of the present invention, there is provided a current detecting device for detecting a first alternating current and a second alternating current having different frequencies that are respectively output from two windings of a dynamo-electric machine having two windings wrapped around the same stator core, including:
first current detecting means for simultaneously detecting a first phase current of a first alternating current and a first phase current of a second alternating current;
second current detecting means for simultaneously detecting a second phase current of the first alternating current and a second phase current of the second alternating current; and
controlling means for setting a current of one winding to zero when detecting a current of the other winding.
According to still another aspect of the present invention, there is provided a current detecting method including:
a current detecting step for simultaneously detecting a plurality of three-phase alternating currents of different frequencies that are respectively output from two windings of a dynamo-electric machine having two windings wrapped around the same stator core;
an estimating step for obtaining estimated values of the respective currents; and
a separation computing step for separating, by each frequency, currents detected by the current detecting step based on outputs of the estimating step.
In a preferred form, the separation computing step includes:
a two-phase alternating current converting step for converting a current detected by the current detecting step into a two-phase alternating current;
a reverse rotation vector multiplying step for multiplying a value obtained by the two-phase alternating current converting step by a vector that rotates in a reverse direction at each frequency; and
a multiplied frequency difference vector subtracting step for subtracting an estimated value multiplied by a vector that rotates at a difference between frequencies from an output of the reverse rotation vector multiplying step.
In another preferred form, the current detecting step includes:
a first current detecting step for simultaneously detecting a first phase current of a first alternating current and a first phase current of a second alternating current;
a second current detecting step for simultaneously detecting a second phase current of the first alternating current and a second phase current of the second alternating current; and
the separation computing step includes:
a two-phase alternating current converting step for converting an output of the first current detecting step and an output of the second current detecting step into two-phase alternating currents;
a first reverse rotation vector multiplying step for multiplying an output of the two-phase alternating current converting step by a unit vector rotating in a reverse direction at a frequency of the first alternating current;
a second reverse rotation vector multiplying step for multiplying an output of the two-phase alternating current converting step by a unit vector rotating in a reverse direction at a frequency of the second alternating current;
a first frequency difference vector multiplying step for multiplying an estimated value of the first alternating current by a unit vector rotating at (a frequency of the first alternating current minus a frequency of the second alternating current);
a first vector subtracting step for subtracting an output of the first frequency difference vector multiplying step from an output of the second reverse rotation vector multiplying step;
a second frequency difference vector multiplying step for multiplying an estimated value of the second alternating current by a unit vector rotating at (a frequency of the second alternating current minus a frequency of the first alternating current); and
a second vector subtracting step for subtracting an output of the second frequency difference vector multiplying step from an output of the first reverse rotation vector multiplying step.
In yet another preferred form, the current detecting step includes:
a first current detecting step for simultaneously detecting a first phase current of a first alternating current and a first phase current of a second alternating current;
a second current detecting step for simultaneously detecting a second phase current of the first alternating current and a second phase current of the second alternating current; and
the separation computing step includes:
a two-phase alternating current converting step for converting an output of the first current detecting step and an output of the second current detecting step into two-phase alternating currents;
a first reverse rotation vector multiplying step for multiplying an output of the two-phase alternating current converting step by a unit vector rotating in a reverse direction at a frequency of the first alternating current;
a second reverse rotation vector multiplying step for multiplying an output of the two-phase alternating current converting step by a unit vector rotating in a reverse direction at a frequency of the second alternating current;
a first estimated value subtracting step for subtracting an estimated value of the first alternating current from an output of the first reverse rotation vector multiplying step;
a first frequency difference vector multiplying step for multiplying an output of the first estimated value subtracting step by a unit vector rotating at (a frequency of the first alternating current minus a frequency of the second alternating current);
a second estimated value subtracting step for subtracting an estimated value of the second alternating current from an output of the second reverse rotation vector multiplying step; and
a second frequency difference vector multiplying step for multiplying an output of the second estimated value subtracting step by a unit vector rotating at (a frequency of the second alternating current minus a frequency of the first alternating current).
The estimated value of the first alternating current and the estimated value of the second alternating current are current command values.
The estimated value of the first alternating current and the estimated value of the second alternating current are first-order lags of the outputs of the first vector subtracting step and the second vector subtracting step.
The estimated value of the first alternating current and the estimated value of the second alternating current are first-order lags of the outputs of the first frequency difference vector multiplying step and the second frequency difference vector multiplying step.
According to another aspect of the present invention, there is provided a current detecting method for detecting a first alternating current and a second alternating current having different frequencies that are respectively output from two windings of a dynamo-electric machine having two windings wrapped around the same stator core, including:
a first current detecting step for simultaneously detecting a first phase current of a first alternating current and a first phase current of a second alternating current;
a second current detecting step for simultaneously detecting a second phase current of the first alternating current and a second phase current of the second alternating current; and
a controlling step for setting a current of one winding to zero when detecting a current of the other winding.